Thermal injection and proportioning head, manufacturing process for this head and functionalization or addressing system comprising this head

ABSTRACT

Injection and proportioning head with at least one thermal injection and proportioning device to supply a determined quantity of liquid, comprising:
         a hollowed out plane substrate ( 21 ) forming a liquid reservoir and covered, in order, by an unconstrained dielectric insulating membrane ( 22, 23 ) with a high thermal resistance, and then an etched semi conducting layer forming the heating resistance ( 25 );   an orifice ( 24 ) enabling fluid communication with said liquid reservoir passing through said membrane and said semi conducting layer;   a photolithographed resin layer in the form of a nozzle ( 27 ) on said membrane, the duct ( 28 ) of said nozzle being in line with said orifice and the volume of said duct being such that the determined quantity of the liquid to be supplied can be controlled.       

     Process for manufacturing this head. 
     Functionalisation or addressing system, particularly for chemical or biochemical micro reactors comprising this head.

DESCRIPTION

This invention relates to a thermal injection and proportioning head,and more precisely a thermal injection and proportioning head comprisingat least one thermal injection and proportioning device with nozzle tosupply and deliver a determined quantity of liquid.

The invention also relates to a manufacturing process for such a head.

Finally, the invention relates to a functionalisation or addressingsystem comprising such a head, particularly for biological or chemicalmicro reactors.

The invention is generally within the field or devices used to depositseveral micro drops of a determined volume of liquid onto a substrate,or to add or inject several micro drops into micro reservoirs.

For example, these liquid drops may be DNA solutions of immunologyreagents, which form miniaturized rows or matrices of drops or testreservoirs, which are used particularly for medical analyses.

For example, it is known that biochips are devices that can be used tomake a very large number of bio analyses in parallel. The principle isto make test micro reservoir matrices in miniaturized form.

Each test point is specific and is the result of a precise mix orcombination of chemical or biochemical elements. These mixes orcombinations may be made by several processes, which may have beenclassified in two main categories.

In the first category of these processes called biochipfunctionalisation processes, the constituents are applied one by one andthe reactions are checked by addressing an action to facilitate orinhibit the reaction on targeted micro reservoirs.

In the second category of biochip functionalisation processes, thespecific constituents are added point by point mechanically into thetargeted micro reservoir; the domain of the invention is related to thissecond category.

Biochip functionalisation processes are divided between firstly “insitu” processes and secondly “ex situ” processes.

The AFFIMETRIX® process is the main in situ synthesis process, in otherwords for example the synthesis of a DNA strand, and is done directly onthe chip, on a solid support. This process is based on in situsynthesis, in other words directly on the chip, of trace nucleotides,for example DNA strands, with methods derived from photolithography.

The surfaces of hybridisation units (UH), modified by a photolabileprotective group, are illuminated through a photolithography mask. UHsthus exposed to light radiation are selectively deprotected and cantherefore be subsequently coupled to the next nucleic acid. Thedeprotection and coupling cycles are repeated until all required tracenucleotides are obtained.

Experiments have already been carried out with other EX SITU processesusing the microelectronic capacities of silicon. The chip comprisesseveral platinum microelectronic electrodes, placed in the bottom ofdishes machined in silicon and addressed individually. The probes, suchas trace nucleotides or DNA strands are coupled to a pyrrole group andare directed by an electric field to the activated electrode, wherecopolymerisation takes place in the presence of free pyrrole and theresult is electrochemical bonding of the probes.

Based on the above, it appears that in situ synthesis processes such asAFFIMETRIX® are used to achieve high densities of hybridising units anduse perfectly controlled techniques compatible with silicon supports.Their major disadvantages are their high cost which makes it impossiblefor small entities such as research laboratories or medical analysislaboratories to use them, and the fact that the low efficiency of thephotodetection reaction means that there is a great deal of redundancyin the sequences present on the chip.

Manufacture is relatively difficult particularly due to thephotolithographic masks and is therefore adapted particularly totargeted objectives with high usage volumes.

In “ex situ” processes, in other words processes in which the DNA strandis synthesised ex situ, each sequence must be pre-synthesisedindependently of the others and then transferred to the support. Theprocedure is long and it is impossible to make a large number ofdifferent sequences on the same chip. The chips made will thus be lowdensity chips.

The second category of addressing processes, that can be qualified asmechanical addressing processes regardless of whether they are ex situor in situ, is represented by many processes that are already marketed,in which robotized, for example pneumatically activated, micropipettesassembled in matrix form, pick up constituents (generally a solutioncontaining DNA fragments or trace nucleotides) and deposit them in theform of precise doses, for example micro drops in test tubes or onminiaturized supports. Glass slides are usually used as support, orstructured supports may be used supporting micro wells etched in thematerial. Each of the bases (A, G, C, T) can also be deposited insequence on the glass slide in the required order.

These conventional techniques are typically used in 96-pin matrices, andhigher densities are possible. The objective with these mechanicalprocesses would be to reach 10 000 dots or more, since there is a largenumber of tests to be carried out in parallel. The number of pins on thesame wafer may be as high as 8000.

The production of micro reservoir matrices is a simple problem that caneasily be solved by microelectronic technologies. We can make:

-   -   simple substrates comprising matrices micro-machined by chemical        or plasma means. Densities of the order of 10 000 dots/cm² are        typical, but 100 000 dots/cm² are also possible;    -   substrates instrumented by electronic or electromechanical        systems; the MICAM chip marketed by the CisBio® Company is a        good example of these substrates. This is the (ex situ) process        illustrated in the first case above.

The more difficult problem is actually to deposit the reagents (probesor others) specifically in each micro reservoir. Several techniques areused for pipetting, including deposition by “pin and ring” by capillarycontact; deviated continuous piezoelectric “ink jet” or “drop ondemand”, or thermal ink jet.

The technique used in thermal ink jet printer heads is very widespreadand very reliable.

In general, a thermal ink jet printer head, for example acting as athermal proportioner micro injector, satisfies the operating principledescribed below.

The liquid to be ejected is confined in a reservoir.

A heating resistance very locally increases the temperature in thereservoir and vaporizes the liquid in contact with the heating area. Thegas bubble thus formed creates an overpressure that ejects a dropoutside the reservoir.

FIG. 1 ideally performs this function.

Under the effect of pressure and capillarity forces, the nozzle (1) withradius r (6) is filled with liquid from a reservoir (4). The nozzle issurrounded by a heat input system at a depth L (2), for example aheating resistance (5) operating by the Joule effect.

Under the effect of the temperature increase at the level (3) and thevaporization of volatile species of the liquid, the top part of theliquid is ejected forming a drop with size v=π²L, where r is the radius(6) of the nozzle (1) and L is the height of the liquid columncorresponding to the depth (2).

Operation is possible continuously, and enables the production of asequence of drops. Operation is also possible drop by drop. The internalradius of the nozzle and its height L are controlled so that drops ofthe order of one picoliter can be produced with injection densities of10⁵ to 10²/cm². The hole density is important because there is nothermal interaction from one hole to the next.

There are three main types of thermal ink jet printer head devices thatapply the principle described above illustrated in FIG. 1.

The first of these devices is the “EDGESHOOTER” device in which twosubstrates, one made of silicon supporting the heating element and onemade of glass, are combined using a glued film and structured byphotolithography. Drops are ejected laterally on the edge of the device.

The second is the “SIDESHOOTER” device for which the structure, similarto the structure of the previous device, comprises a silicon substrateand a glued film, but which are covered by a metallic plate on which thenozzles are made. Drops are ejected facing the heating element.

The third is the “BACKSHOOTER” device in which the print head is madefrom oriented silicon substrates <110>.

The ducts through which the ink passes are made by anisotropic etchingof one side of the substrate, while thin films are deposited on theother side that enable production of the membrane supporting the heatingelement and the electronics. The nozzles are located at the centre ofthe membrane and the heating elements are located on each side of themembrane. Resolution can be as high as 300 dpi (dots per inch) and 600dpi.

In all cases, in other words for the three devices, the print head iscomposed of a single line comprising only about fifty nozzles each about20 μm×30 μm. The velocity of the drops at ejection varies from 10 to 15m/s.

For example, this type of device is described in documents PCT/DE91/00364, EP-A-0 530 209, . . . DE-A-42 14 554, DE-A-42 14555 andDE-A-42 14556.

All these thermal ink jet print head devices, particularly when used foran application such as a thermal proportioning micro injector head, havethe serious disadvantage of large heat losses.

Consequently, it is only possible to make heads with a single line ofholes rather than a matrix. Therefore, the densities and resolutions arenot nearly sufficient.

Therefore, there is a need for an injection and proportioning headcomprising a thermal injection and proportioning device that does nothave this serious disadvantage.

There is also a need for an injection and proportioning head that canachieve densities and resolutions at least equivalent to those obtainedwith in situ addressing or synthesis systems such as AFFIMETRIX® withouthaving these disadvantages. At the moment, no mechanical addressingsystem is capable of achieving these densities and resolutions.

The purpose of this invention is to provide an injection andproportioning head for a thermal injection proportioning device which,among others, satisfies all the needs mentioned above.

Another purpose of this invention is to provide a thermal injection andproportioning head that does not have the disadvantages, limitations,defects and drawbacks of injection and proportioning heads according toprior art and which solves the problems that arise for injection andproportioning heads according to prior art.

This and other purposes are achieved according to the invention by aninjection and proportioning head comprising at least one thermalinjection and proportioning device to supply a given quantity of liquid,said device comprising:

-   -   a hollowed out plane substrate forming a liquid reservoir and        covered, in order, by an unconstrained dielectric insulating        membrane with a high thermal resistance, and then an etched        semi-conducting layer forming the heating resistance;    -   an orifice allowing fluid communication with said liquid        reservoir passing through said membrane and said semi conducting        layer;    -   a layer of photolithographed resin in the form of a nozzle on        said membrane, the duct for said nozzle being located along the        same line as said orifice and the volume of said duct being used        to control the quantity of liquid to be supplied.

According to the invention, heating is done on an unconstraineddielectric insulating membrane with a high thermal resistance, andconsequently heat losses are very much reduced and as a result it willbe possible to make a head comprising a two-dimensional matrix ofnozzles or holes, rather than simply a simple line or row.

In other words, the structure of the device according to the inventioncomprising three layers on the substrate and which has never beenmentioned in prior art is such that, surprisingly and optimally, theheat generated only very slowly passes through the membrane that has ahigh or very high thermal resistance. Thus one of the majordisadvantages of similar devices according to prior art, namely highheat losses, is eliminated. Injection-proportioning devices in a headcan be brought closer together and have a significantly higher densitythan in prior art. Thus, heads according to the invention can be used tomake two-dimensional matrices of nozzles or injection-proportioningholes with a high density, for example 10⁴/cm².

Furthermore, the volume to be delivered and supplied in the deviceaccording to the invention is easily and very precisely determined bythe volume of the nozzle duct and which is easily made fromphotolithographed resin.

The head according to the invention can supply perfectly definedquantities of liquid at perfectly defined points, for example with adensity of 10⁴ to 10⁵/cm², which has never been achieved in the pastwith mechanical devices of the thermal micropipette type.

The determined quantity of liquid to be supplied and delivered by thedevice is usually between 1 and a few nl, up to 100 μl. This is why theterm “micropipette” is generally used.

The substrate is generally made of monocrystalline silicon, possiblydoped.

Advantageously, according to the invention, the unconstrained dielectricinsulating membrane with a high thermal resistance is composed of astack of two layers, with thicknesses such that the (thermo)mechanicalstress in the stack is zero.

The membrane can thus be composed of a stack of a first layer of SiO₂ onthe substrate, followed by a second layer of SiN_(x) where x ispreferably 1.2.

For example, the semi-conducting layer could be polysilicon or dopedpolycrystalline silicon. The doping element could advantageously bephosphorus.

It is also possible to provide a chemically and thermally insulatinglayer between the etched semi-conducting layer forming a heatingresistance and the layer of photolithographed resin in the form of anozzle.

Advantageously, the head according to the invention comprises several ofsaid thermal injection and proportioning devices.

Preferably, this is made possible by the structure of the deviceaccording to the invention, said devices and consequently the holes ornozzles are arranged in the form of a two-dimensional matrix.

When the head comprises several thermal injection and proportioningdevices, the number of these devices may for example be 10² to 10⁵ for ahead area of 10 mm² to 1.5 cm².

Advantageously, the head according to the invention is formed entirelyfrom a single substrate; from a single insulating membrane,semi-conducting layer and photolithographed resin layer.

The invention also relates to a process for manufacturing an injectionand proportioning head according to claim 1, in which the followingsteps are carried out in sequence:

-   -   an unconstrained dielectric insulating layer or membrane with a        high thermal resistance is made on the two faces of a plane        substrate;    -   a semi conducting layer is deposited on the dielectric        insulating layers;    -   a pattern of a photosensitive resin is made on a semi conducting        layer located on the top face of the substrate, and then the        areas of the unconstrained semi conducting layer not protected        by resin are eliminated, thus making a heating resistance        pattern;    -   a chemically and thermally insulating layer may be made on the        top face of the substrate;    -   an orifice is made in the semi-conducting layer, in the        unconstrained dielectric insulating layer with a high thermal        resistance on the top face of the substrate, and possibly in the        chemically and thermally insulating layer;    -   a thick layer of photosensitive resin is deposited on the top        face of the substrate and it is photolithographed to make a        nozzle in line with the orifice;    -   openings are made in the dielectric insulating layer on the back        of the substrate;    -   the areas of the back face of the substrate not protected by the        dielectric insulating layer are etched, in order to create a        reservoir for the liquid to be ejected and to release the        membrane.

The substrate may be made of a monocrystalline silicon, possibly doped.

Advantageously, the dielectric insulating membrane is made bysuccessively depositing two layers forming a stack on the substrate, thethicknesses of the two layers being such that the (thermo)mechanicalstress in the stack is zero.

The first layer may be a layer of SiO₂ and the second layer may be alayer of SiN_(x).

The semi conducting layer is generally made of polysilicon orpolycrystalline silicon, preferably doped by phosphorus.

The areas of the semi conducting layer not protected by thephotosensitive resin are preferably eliminated by a plasma etchingprocess.

The heating resistance pattern is usually in the form of a squaresurrounding the ejection head, but it may also have any geometryenabling a local but sufficient temperature increase.

The chemically and thermally insulating layer is usually made of a layerof silicon oxide, of the Spin On Glass (SOG) type.

The orifice or hole in the chemically and thermally insulating layer (ifthere is such a layer), in the semi-conducting layer and in thedielectric insulating layer may be made by a chemical etching and/orplasma etching process depending on the layer.

The openings in the dielectric insulating layer on the back face of thesubstrate are preferably made by photolithography.

The unprotected areas of the back face of the substrate are usuallyetched by a chemical process, but may be etched by plasma.

Finally, the invention relates to a functionalisation or addressingsystem, particularly for chemical or biochemical micro reactorscomprising the ejection and proportioning head described above.

In this type of system, the proportioned injected liquid may for examplebe a solution of reagents such as phosphoramidites, etc.

This type of system according to the invention overcomes thedifficulties mentioned above for such systems either of the “in situ” or“ex situ” type.

In particular, systems according to the invention in which the headscomprise injection device matrices and therefore nozzles have thefollowing advantages:

-   -   the possibility of functionalising a large number of small        hybridisation units (<100 μm×100 μm) in parallel;    -   use of the chemical method and therefore improvement of        synthesis yields;    -   flexibility of the device to make the required sequences on        request, without any cost effectiveness threshold problem;    -   low cost.

At the present time, the use of biochips is limited to a few largecompanies. The system according to the invention makes this use possibleby all potential customers.

Thus, apart from genomics or biochips, heads and systems according tothe invention can be used in combinational chemistry or pharmaceuticalformulation applications.

The invention will now be described in detail. The following descriptionis given for illustrative and non limitative purposes with reference tothe appended drawings, wherein:

FIG. 1 is a diagrammatic sectional view of an ideal theoretical devicefor a thermal proportioning micro injector;

FIG. 2 is a diagrammatic sectional view of a thermal proportioning microinjector according to the invention; and

FIGS. 3 to 12 are diagrammatic sectional views that illustrate thedifferent steps in the process according to the invention.

The structure of the thermal proportioning micro injector in FIG. 2comprises firstly a monocrystalline silicon support (11), preferably amonocrystalline silicon doped by an element, particularly such aschemical etching of silicon, in basic solutions if possible.

For example, the doping element may be chosen among boron andphosphorus.

There is a membrane on the support composed of a first insulating layerof SiO₂ (22) and a second layer of SiN_(x) (23) where x=1.2. Therelative thickness of each of these insulating layers is controlled suchthat there is very little and preferably no residual mechanical stresswith the monocrystalline silicon support.

Furthermore, the thickness of the SiN_(x) layer is preferably such thatthe residual mechanical stress resulting from the stack of these twolayers is theoretically zero.

The thickness of the SiO₂ layer is usually 0.8 to 1.6 μm, whereas thethickness of the SiN_(x) layer is usually 0.2 to 0.9 μM.

A small hole (24) is formed in this membrane. This hole is usuallycircular, for example with a diameter from 5 to 50 microns.

The membrane supports an integrated heating resistance (25), usuallymade of strongly doped polycrystalline silicon in order to achieve thelowest possible electrical resistivity.

The doping element of this polycrystalline silicon will for example bechosen from among phosphorus and boron with a content of 10¹⁹ to 10²⁰at/cm³.

This type of heating resistance may locally warm up to high temperaturesof up to several hundred of degrees, for example from 40 to 500° C.

The heating resistance is thermally and chemically insulated, preferablyby a layer of silicon oxide (26), for example a “spin on glass” typelayer of silicon oxide.

A nozzle is added onto the insulating silicon oxide layer, this nozzle(27) is usually made from a photosensitive resin such as SV8 resin(CIPEC®), due to the manufacturing process used.

The duct (28) of the nozzle (27) is in line with the hole made in themembrane and the insulating layer, for example made of silicon oxide.

The manufacturing process according to the invention comprises thefollowing steps illustrated in FIGS. 3 to 12:

1. The substrate or nozzle support (21) is a double sided polishedsilicon wafer, for example 350 to 500 μm thick with dimensions 10 to 15cm. The dimensions of the wafer are large enough to make 50 to 1000thermal proportioning micro injectors. As already mentioned above, it isa monocrystalline silicon support, preferably doped by an element suchthat chemical etching of the doped silicon is possible, particularly inbasic solutions such as KOH or TMAH. Therefore the doping element may bechosen from among boron or phosphorous, with a content of 10¹⁶ to 10¹⁸at/cm³.

2. A silicon oxide layer (22), for example with a thickness between 0.8to 1.6 μm, is made on the two faces of the wafer (FIG. 3).

The oxide layer (22) is obtained by direct oxidation of silicon, usuallyat a temperature of 1150° C.

3. A layer of SiN_(x) (23) is then deposited on the two faces of thewafer (FIG. 4). In the formula SiN_(x), x is a real number x=1.2. Thethickness of this layer is such that the residual mechanical stressresulting from the stack of the SiO₂ layer and the SiN_(x) layer istheoretically zero. Thus, the thickness of the SiN_(x) layer is usuallybetween 0.2 and 0.9 μm.

The deposit is usually made using a vapour phase deposition technique.

The layers of SiO₂ and SiN_(x) present on the back face of the siliconwafer will be used at the end of masking layer manufacturing processduring chemical etching to release the membrane.

4. A layer of polysilicon or polycrystalline silicon (25) is thendeposited on the two faces of the wafer (FIG. 5). The thickness of thislayer is usually between 0.5 and 1.5 μm. The deposit is usually madeusing a vapour phase deposition technique.

This layer (25) is then doped, for example by diffusion of phosphorus toachieve the lowest possible electric resistivity. Therefore, the contentof a doping agent such as phosphorus in the polysilicon layer (25), willusually be between 10¹⁹ and 10²⁰ at/cm³. The diffusion doping operationis usually done under the conditions T=950° C. for 25 minutes.

5. The polysilicon layer deposited in step 4 is covered with aphotosensitive resin (29) in a square pattern and over a thickness offor example 1 to 3 μm. For example, this photosensitive resin may bechosen from among CLARIANT resins.

The photosensitive resin (29) is generally deposited using a centrifugaldeposition technique.

The photosensitive resin (29) is selectively etched using aphotolithography technique. Polysilicon areas not protected by the resinare eliminated by plasma etching.

The pattern thus formed is used to make a heating resistanceapproximately in the form of a ring (FIGS. 6 and 7).

6. For example, the polysilicon resistance is covered with a spin onglass type silicon oxide layer (26), usually 100 to 200 nm thick, sothat it is electrically and chemically protected from the outsideenvironment (FIG. 8).

7. A hole (24) that will form the ejection orifice, is made at thecentre of the heating resistance by chemical etching, for example, in aHF solution of silicon oxide (“spin on glass”) then plasma etching ofSiN_(x) and then once HF chemical etching of the silicon oxide layer(FIG. 9).

This hole (24) is usually circular and has a diameter of between 5 and50 μm.

8. A thick layer of photosensitive resin (27) is based on the spin onglass silicon oxide layer (26). A thick layer usually means a layer witha thickness of between 1 μm and 100 μm.

The photosensitive resin is usually the SV8 resin made by CITEC® and thedeposition technique is deposition by centrifuging.

After the deposition, the resin layer is photolithographed in order tomake the ducts (28) of the nozzles surrounding the hole or injectionorifice (FIG. 10).

9. Openings (31) are formed in the SiO₂ and SiN_(x) layers present onthe back face using a photolithography process, already presented above(FIG. 11).

10. Chemical etching of areas not protected by the SiO₂/SiN_(x) doublelayer, for example in a solution of KOH or TMAH, firstly excavates thereservoir (32) in the silicon substrate, to hold the liquid to beinjected and also releases the membrane supporting the heating deviceand the ejection nozzle (FIG. 12).

1. An injection and proportioning head comprising at least one thermalinjection and proportioning device to supply a determined quantity ofliquid, said device comprising: a hollowed out plane substrate (21)forming a liquid reservoir and covered, in order, by a directlydeposited unconstrained dielectric insulating membrane (22, 23) with ahigh thermal resistance, a directly deposited etched semi conductinglayer forming the heating resistance (25); an orifice (24) enablingfluid communication with said liquid reservoir passing through saidmembrane and said semi conducting layer, and thereafter aphotolithographed resin layer in the form of a nozzle (27) on saidmembrane, the duct (28) of said nozzle being in line with said orificeand the volume of said duct being such that the determined quantity ofthe liquid to be supplied can be controlled.
 2. Injection andproportioning head according to claim 1, in which the determinedquantity of liquid is 1 nl to 100 μl.
 3. Head according to claim 1, inwhich the substrate comprises monocrystalline silicon.
 4. Head accordingto claim 1, in which the semi conducting layer is made of dopedpolysilicon or polycrystalline silicon.
 5. Head according to claim 4, inwhich the polysilicon or the polycrystalline silicon is doped byphosphorus.
 6. Head according to claim 1, in which a chemically andthermally insulating layer is also provided between the etched semiconducting layer and the photolithographed resin layer in the form of anozzle.
 7. Head according to claim 1, comprising several thermalinjection and proportioning devices.
 8. Head according to claim 7, inwhich said devices are arranged in the form of a two-dimensional matrix.9. Head according to claim 7, comprising 10² to 10⁵ injection devices.10. Head according to claim 7, in which the head is formed entirely froma single substrate; from a single insulating membrane, semi conductinglayer, a chemically and thermally insulating layer if there is one, anda photolithographed resin layer.
 11. Functionalisation or addressingsystem, particularly for chemical or biochemical micro reactors,comprising the injection and proportioning head according to claim 1.12. Use of the system according to claim 11 in techniques usingbiochips, genomics, combinational chemistry of pharmaceuticalformulation.
 13. Use of the head according to claim 1, in techniquesinvolving biochips, genomics, combinational chemistry or pharmaceuticalformulation.
 14. Head according to claim 1, in which the substratecomprises doped monocrystalline silicon.
 15. An injection andproportioning head comprising at least one thermal injection andproportioning device to supply a determined quantity of liquid, saiddevice comprising: a hollowed out plane substrate (21) forming a liquidreservoir and covered, in order, by an unconstrained dielectricinsulating membrane (22,23) with a high thermal resistance composed of astack of two layers, the thickness of which are such that the(thermo)mechanical stress in the stack is zero, an etched semiconducting layer forming the heating resistance (25), an orifice (24)enabling fluid communication with said liquid reservoir passing throughsaid membrane and said semi conducting layer, a photolithographed resinlayer in the form of a nozzle (27) on said membrane, the duct (28) ofsaid nozzle being in line with said orifice and the volume of said ductbeing such that the determined quantity of the liquid to be supplied canbe controlled.
 16. Head according to claim 15, in which the membrane iscomposed of a stack comprising, in order, a first layer of SiO₂ on thesubstrate, followed by a second layer of SiN_(X), where x is preferably1.2.
 17. Manufacturing process for an injection and proportioning headaccording to claim 1, in which the following steps are carried out insequence: an unconstrained dielectric insulating layer or membrane witha high thermal resistance is directly made on the two faces of a planesubstrate; a semi conducting layer is directly deposited on thedielectric insulating layers; a pattern of a photosensitive resin ismade on a semi conducting layer located on the top face of thesubstrate, and then the areas of the unconstrained semi conducting layernot protected by resin are eliminated, thus making a heating resistancepattern; a chemically and thermally insulating layer may be made on thetop face of the substrate; an orifice is made in the semi-conductinglayer, in the unconstrained dielectric insulating layer with a highthermal resistance on the top face of the inorganic plane substrate, andpossibly in the chemically and thermally insulating layer; a thick layerof photosensitive resin is deposited on the top face of the substrateand it is photolithographed to make a nozzle in line with the orifice;openings are made in the dielectric insulating layer on the back of thesubstrate; the areas of the back face of the inorganic plane substratenot protected by the dielectric insulating layer are etched, in order tocreate a reservoir for the liquid to be ejected and to release themembrane.
 18. Process according to claim 17, in which the substrate ismade of monocrystalline silicon.
 19. Manufacturing process for aninjection and proportioning head according to claim 1, in which thefollowing steps are carried out in sequence: an unconstrained dielectricinsulating membrane is formed on both sides of the substrate forming astack, the thickness of the two layers being such that the(thermo)mechanical stress of the stack is zero with a high thermalresistance is made on the top face and back face of a plane substrate; asemi conducting layer is deposited on the dielectric insulatingmembrane; a pattern of a photosensitive resin is made on a semiconducting layer located on the top face of the substrate, and then theareas of the semi conducting layer not protected by resin areeliminated, thus making a heating resistance pattern; a chemically andthermally insulating layer may be made on the face of the substrate; anorifice is made in the semi-conducting layer, in the unconstraineddielectric insulating membrane with a high thermal resistance on the topface of the plane substrate, and possibly in the chemically andthermally insulating layer; a thick layer of photosensitive resin isdeposited on the top face of the substrate and it is photolithographedto make a nozzle in line with the orifice; openings are made in thedielectric insulating membrane on the back of the substrate; areas ofthe back face of the substrate are etched, in order to create areservoir for the liquid to be ejected and to release the membrane. 20.Process according to claim 19, in which the first layer of the stack isan SiO₂ layer and the second layer is an SiN_(X) layer wherein x isabout 1.2.
 21. Process according to claim 17, in which the semiconducting layer is made of doped polysilicon or polycrystallinesilicon.
 22. Process according to claim 17, in which the areas of thesemi conducting layer not protected by the photosensitive resin areeliminated using a plasma etching process.
 23. Process according toclaim 17, in which the orifice in the chemically and thermallyinsulating layer, if any, in the semi conducting layer and in thedielectric insulating layer, is made using a chemical etching and/orplasma etching process, depending on the layer.
 24. Process according toclaim 17, in which the openings in the dielectric insulating layer onthe back face of the substrate are made by photolithography.
 25. Processaccording to claim 17, in which the unprotected areas on the back faceof the substrate are etched by a chemical process.
 26. Process accordingto claim 17, in which the substrate comprises doped monocrystallinesilicon.